1. Field of the Invention
This invention relates to an improved process for the manufacture of a blend composition of a neutralized sulfonated elastomeric polymer which includes the steps of sulfonating an elastomeric polymer dissolved in a solvent to form an acid form of the sulfonated elastomeric polymer. The solution of the acid form of the sulfonated elastomeric polymer is quenched with an oxirane to form a polymeric hydroxyalkyl sulfonate. A non-polar backbone process oil is added thereby plasticizing the polymeric backbone of the hydroxyalkyl sulfonate. The hydroxyalkyl sulfonate is reacted with a metal carboxylate to form equivalent portions of a solid gel-free neutralized sulfonated elastomeric polymer and a hydroxyalkyl carboxylate ester.
These blend compositions can be readily processed due to their superior rheological properties on conventional plastic fabrication equipment into elastomeric articles having excellent physical properties and desirable rubbery characteristics.
The hydroxyalkyl esters of this invention may be schematically represented as follows: ##STR1## wherein .about.C.about. is one or more carbon atoms in one or more molecules comprising a polymer and is in the polymer backbone-chain of carbon atoms, or is in an acyclic, alicyclic, or aromatic group which is pendant to the backbone chain; R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, C.sub.1 to C.sub.18 straight and branched chain acyclic, alicyclic, aryl, alkylaryl, arylalkyl groups and functional derivatives thereof.
Products which have a limited concentration of ionic groups covalently bonded to one or more carbon atoms of one or more molecules comprising a polymer, when partially or completely neutralized with mono or polyvalent cations such as sodium, zinc, magnesium, lead, ammonium and quaternary ammonium compounds are generally referred to as ionomers. The ionic groups can be covalently bonded to carbon atoms comprising the backbone chain of the polymer, which chain of carbon atoms may be interrupted by hetero atoms such as oxygen, nitrogen and sulfur, or the ionic groups can be bonded to acyclic, alicyclic or aromatic groups which are pendant to the backbone chain. Solid gel-free ionomers differ from covalently crosslinked elastomers, such as vulcanized rubber, in that while ionomers can be elastomeric at ordinary temperatures, at elevated temperatures they can be extruded, compression molded, blow molded, sheeted, vacuum formed and injection molded.
Sulfonated polymers i.e. those containing free sulfonic acid groups are known to be relatively unstable and are difficult to process in safety or without degradation in conventional plastic or rubber equipment at elevated temperatures. Except for this tendency to degrade it would be advantageous to process the free acid since the relatively weak ionic associations among the acid groups result in a low polymer viscosity permitting easy mixing with neutralizing agents extender oils, plasticizers, fillers, and other polymers. Such extended systems can then be mixed and reacted with a neutralizing agent such as metallic oxides, hydroxides, and alkoxides or salts of weak acids such as an acetate or stearate to yield the ionomer.
On the other hand, if the sulfonated polymer is first neutralized with a counterion and the ionomeric product isolated, it is found to possess an extraordinarily high viscosity even at elevated temperatures commonly used for processing thermoplastic polymers in conventional equipment and must be mixed with other materials by solution techniques.
A major object of this invention is the preparation of low viscosity, thermally and hydrolytically stable esters of sulfonated polymers which are readily convertible to ionomers by reaction with a basic substance. A further object of this invention is the preparation of oil extended ionomeric blend compositions which comprises reacting a polymer having one or more sulfonic acid groups covalently linked or bonded to one or more carbon atoms in one or more molecules comprising said polymer with an oxirane to form a hydroxyalkyl ester, then adding an oil and then reacting said ester with a basic substance selected from the group consisting of mono and polyvalent metallic oxides, hydroxides, alkoxides and salts of acids having a lower K.sub.a then the sulfonic acid. These, and other objects of this invention will be further apparent in the detailed description of the invention which follows below.
2. Description of the Prior Art
The reaction of an oxirane (e.g. ethylene oxide) with a sulfonic acid to form a hydroxyethyl ester is old in the art. U.S. Pat. No. 2,208,581 discloses the preparation of surface active agents by the reaction of low molecular weight sulfonic acids with a compound containing an olefin oxide.
In a first copending application concerning preparation of ionomeric latex epoxides are used to quench the sulfonation reaction and allow the cement to be processable in a unique latex process. However, this copending application fails to teach a method for the isolation of a solid, gel free, hydrolytically stable polymeric hydroxyalkyl sulfonate having desirable physical and rheological properties, wherein these polymeric sulfonates are readily convertible to metal sulfonates during and after processing thereby permitting fabrication on conventional plastic type equipment to a variety of useful articles. Furthermore, it is completely unpredictable that a solid, gel free, hydrolytically stable polymeric hydroxyalkyl sulfonate is capable of being isolated in a steam stripping operation under acidic conditions and at higher temperatures based upon the published literature on the hydrolytic stability of low molecular weight alkyl sulfonates. No references have been found in the chemical or patent literture for the preparation of hydroxyalkyl esters of polymeric sulfonic acids or for the preparation of ionomers from these esters by reaction with a basic compound or salt of an acid having a lower K.sub.a than the sulfonic acid.
In another copending application, Ser. No. 855,763, filed Nov. 29, 1977, entitled "Polymeric Hydroxyalkyl Sulfonates" herein incorporated by reference, the preparation of polymeric hydroxyalkyl sulfonates are described wherein an acid form of a sulfonated polymer is reacted with an oxirane having the general formula: ##STR2## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen and C.sub.1 to C.sub.18 straight and branched chain acyclic, alicyclic, aryl, alkylaryl, arylalkyl radicals and functional derivatives thereof. The improved blend compositions of the present instant invention provide materials of superior rheological properties.